104 lines
3.5 KiB
Plaintext
104 lines
3.5 KiB
Plaintext
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/*
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* Copyright 2012 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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// To generate callback.h from callback.h.pump, execute:
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// /home/build/google3/third_party/gtest/scripts/pump.py callback.h.pump
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// Callbacks are callable object containers. They can hold a function pointer
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// or a function object and behave like a value type. Internally, data is
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// reference-counted, making copies and pass-by-value inexpensive.
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//
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// Callbacks are typed using template arguments. The format is:
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// CallbackN<ReturnType, ParamType1, ..., ParamTypeN>
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// where N is the number of arguments supplied to the callable object.
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// Callbacks are invoked using operator(), just like a function or a function
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// object. Default-constructed callbacks are "empty," and executing an empty
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// callback does nothing. A callback can be made empty by assigning it from
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// a default-constructed callback.
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//
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// Callbacks are similar in purpose to std::function (which isn't available on
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// all platforms we support) and a lightweight alternative to sigslots. Since
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// they effectively hide the type of the object they call, they're useful in
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// breaking dependencies between objects that need to interact with one another.
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// Notably, they can hold the results of Bind(), std::bind*, etc, without needing
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// to know the resulting object type of those calls.
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//
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// Sigslots, on the other hand, provide a fuller feature set, such as multiple
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// subscriptions to a signal, optional thread-safety, and lifetime tracking of
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// slots. When these features are needed, choose sigslots.
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//
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// Example:
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// int sqr(int x) { return x * x; }
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// struct AddK {
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// int k;
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// int operator()(int x) const { return x + k; }
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// } add_k = {5};
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//
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// Callback1<int, int> my_callback;
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// cout << my_callback.empty() << endl; // true
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//
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// my_callback = Callback1<int, int>(&sqr);
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// cout << my_callback.empty() << endl; // false
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// cout << my_callback(3) << endl; // 9
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//
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// my_callback = Callback1<int, int>(add_k);
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// cout << my_callback(10) << endl; // 15
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//
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// my_callback = Callback1<int, int>();
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// cout << my_callback.empty() << endl; // true
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#ifndef WEBRTC_BASE_CALLBACK_H_
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#define WEBRTC_BASE_CALLBACK_H_
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#include "webrtc/base/refcount.h"
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#include "webrtc/base/scoped_ref_ptr.h"
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namespace rtc {
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$var n = 5
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$range i 0..n
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$for i [[
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$range j 1..i
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template <class R$for j [[,
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class P$j]]>
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class Callback$i {
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public:
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// Default copy operations are appropriate for this class.
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Callback$i() {}
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template <class T> Callback$i(const T& functor)
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: helper_(new RefCountedObject< HelperImpl<T> >(functor)) {}
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R operator()($for j , [[P$j p$j]]) {
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if (empty())
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return R();
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return helper_->Run($for j , [[p$j]]);
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}
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bool empty() const { return !helper_; }
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private:
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struct Helper : RefCountInterface {
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virtual ~Helper() {}
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virtual R Run($for j , [[P$j p$j]]) = 0;
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};
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template <class T> struct HelperImpl : Helper {
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explicit HelperImpl(const T& functor) : functor_(functor) {}
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virtual R Run($for j , [[P$j p$j]]) {
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return functor_($for j , [[p$j]]);
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}
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T functor_;
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};
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scoped_refptr<Helper> helper_;
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};
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]]
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} // namespace rtc
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#endif // WEBRTC_BASE_CALLBACK_H_
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